As a vibration control device for beam-and-column frame, one which is set forth in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2003-90,144 (or Patent Literature No. 1) has been heretofore available conventionally. The vibration control device illustrated in FIG. 2 of Patent Literature No. 1 comprises a plastic body being fixed to an upper beam, and a pair of braces connecting this plastic body with a lower beam. That is, it is possible to absorb seismic energies because the plastic body deforms in a case where a beam-and-column frame has deformed horizontally; as a result, it is one which can keep the beam-and-column frame from vibrating.
However, in the constitution according to FIG. 2 of Patent Literature No. 1, one of the braces undergoes tensile deformations, but the other one of the braces undergoes compression deformations, upon the beam-and-column frame undergoing horizontal deformations. That is, it is needed that the braces have rigidity that can withstand the compression deformations. Therefore, there is such a problem that the cross section of the braces should be enlarged.
Here, in FIG. 1 of Patent Literature No. 1, it is devised so as to make compression forces less likely to be applied to the braces. However, it is difficult to produce only shear deformations in the plastic body by this constitution, and so the load-deformation characteristic (e.g., the Q-δ characteristic) at the time of applying repetitive loads horizontally thereto becomes a slippage type (being also referred to as a non-spindle type, or a non-complete elasto-plasticity type, in general).
The “application of repetitive loads” is that the following are repeated: after applying a maximum load in one of the horizontal directions, the aforesaid load is decreased gradually; whereas, another load in the other one of the horizontal directions is increased gradually until the load being applied in the other horizontal direction becomes the maximum load, and then the load being applied in the other horizontal direction is decreased gradually. And, the “slippage type” is a state where a behavior upon decreasing the load being applied in one of the horizontal directions, and another behavior upon increasing the load being applied in the other one of the horizontal directions do not make a continuous behavior, but make a step-shaped, namely, slipped behavior. Moreover, in the case of the slippage type, the behaviors do not become continuous but become stepwise similarly even when the directions of the load applications are reversed contrary to those above.
Note herein that making the load-deformation characteristic at the time of applying repetitive loads into a so-called spindle type (being also referred to as a complete elasto-plasticity type, in general), alternatively, making it approach a spindle type, leads to making the ability of absorbing energies much higher. This is because the restorability becomes favorable by making the characteristic into a spindle type. That is, in the constitution according to FIG. 1 of Patent Literature No. 1, even if it is possible not to make any compression forces act on the braces, the restorability is not favorable because the load-deformation characteristic becomes a slippage type when the plastic body undergoes, in addition to shear deformations, deformations as well in the axial directions of the braces in which tensile forces act.
Moreover, as another vibration control device, one which is illustrated in FIG. 4 of Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2006-152,722 (or Patent Literature No. 2) has been available. The vibration control device according to FIG. 4 of Patent Literature No. 2 is equipped with a fixed plate (23) being disposed upright to a lower beam, two pieces of movable plates (24) being supported swingably so as to interpose the fixed plate (23) therebetween, a pair of braces (5, 6) for connecting the movable plate (24) with an upper beam, a viscoelastic damper (21) being interposed between the fixed plate (23) and the movable plate (24) over the entirety. And, the paired braces (5, 6) intersect with each other adjacent to their middles.
In this constitution, tensile forces and compression forces act alternately on the braces (5, 6), as set forth in paragraph [0016] of Patent Literature No. 2, when horizontal external forces act on a beam-and-column frame. Therefore, it is needed that the braces (5, 6) have rigidity that withstand the acting compression forces. That is, in the same manner as the constitution according to FIG. 2 of Patent Literature No. 1, the constitution being set forth in Patent Literature No. 2 has such a problem that the cross section of the braces should be enlarged.
Furthermore, there is such a fear that the fixed plate (23), and the movable plate (24) undergo such deformations that they pop out in the normal direction with respect to a plane of the beam-and-column frame, when tensile forces or compression forces act on the braces (5, 6). This fear makes one of the causes that the vibration control device declines in the durability. This problem not only arises from the constitutions of the fixed plate and movable plate themselves, namely, their small rigidities against the deformations in the normal direction with respect to a plane of the beam-and-column frame, but also arises from the tensile forces and compression forces that act on the braces (5, 6) alternately.    Patent Literature No. 1: Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2003-90,144; and    Patent Literature No. 2: Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2006-152,722